A series of experiments is proposed for investigating the nature of the basic capacities underlying speech perception in infants and the subsequent development of these capacities in the process of acquiring a native language. The proposed studies have several objectives. First, they are intended to explore the nature of the sensory and perceptual mechanisms underlying speech processing, especially as these relate to other cognitive and perceptual capacities. In particular, the influence of memory and attentional demands on the development of speech perception win be explored. Second, we also plan to investigate the contributions of infants' speech perception capacities to the acquisition of language. Our focus in this area will be on the way that sensitivity to the sound patterns of the native language could provide infants with important information about the nature and organization of important grammatical units in the native language. The third objective of our proposed studies is to determine the way that the representation of speech changes as information is acquired about the structure and organization of words and sounds in the native language. Our strategy here is to delineate the kinds of information that are encoded in infants' representations of speech, to follow any changes that occur to the sensitivity of the characteristic sound patterns of the native language and describe what their impact is on the representation of speech sounds by language learning infants. Finally, we want to explore possible relations between the infant's processing of prosodic and phonetic levels of language. A general issue here concerns whether sensitivity to these levels develops more or less independently or whether there are mutual influences during the early stages of language acquisition. To achieve these ends, we plan to employ a variety of different methodologies suitable for testing infants during the first year of life. These include sucking, visual preference and operant headturning procedures. In the past, one obstacle to understanding how speech perception capacities function in language acquisition is that the range of situations in which these capacities were assessed were quite restricted as compared to the natural environment. We plan to vary the memory and attentional demands of our tasks in an effort to learn more about the way that such capacities function in the real world. Speech perception is certainly one of the basic prerequisites for normal human communication. Our research is intended to contribute to the understanding of this fundamental ability. The research has practical relevance for those studying communication disorders. Information about the way that speech perception develops provides a baseline for assessing abnormalities that may arise. Early identification of such abnormalities is essential to the formulation of effective treatment programs.